We are shipping official version heatsink solution (8mm) to all the Kickstarters ,however, we are very keen on improving it even more. OK we are a little bit maniac.
At this moment, CPU drop to 480MHz when it starts throttling ( it means when CPU temperature reaches 90C, the CPU frequency starts going down to 480MHz until CPU temperature reduces to 80C, then CPU frequency starts going up again); our goal is to set CPU at 1GHz above during throttling ( no specific time plan yet).

You can refer below for our test condition:
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1. room temperature at 25 C
2. Use Burn-in test program V8.1 for board stress, and HW Monitor program for status checking
3. Test condition and setting in burn-in program http://i.imgur.com/nBZROzO.png
4. Run 48 hrs non-stop and monitor CPU core temperature and frequency by HW monitor program
5. Generate report
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We will soon upload 3D file of UP board+ current 8mm heatsink in community; and we will phase in new heatsink once we find a way to keep it at 1GHz above during throttling. Basically it should not impact your chassis design, because our goal is the heatsink height should be always lower than than USB connector.

How much current you can draw from the 3.3/5V pins? I'm currently driving a 80mm fan from the 5V pins and seems to work just fine, but I'm a bit worried it might break something. I guess the fan uses less than 100mA @ 5V.

Thanks aaeon. Yes, my intention was just to ask about the official upper limits for drawing current from the power pins, in general (maybe it could mentioned in the GPIO wiki/documentation page). Apparently the stuff connected to the 5V pins can use quite a lot of power although I'd probably use a dedicated power adapter if it needs more than 1A. I had an old two pin fan from my old PC so it was easier to connect it to the GPIO pins after reversing the pin order from the fan's socket.

Has there been any questions related to higher operating temperature range like down to -25 celsius instead of 0 only? That would make upboard more attractive for outdoor applications in some cold regions.